Many illnesses or conditions require a constant level of medicaments or agents in vivo to provide the most effective prophylactic, therapeutic or diagnostic results. In the past, medicaments were given in doses at intervals which resulted in fluctuating medication levels.
Attempts to control and steady medication levels have more recently included the use of many biodegradable substances, such as poly(lactide) or poly(lactide-co-glycolide) microspheres containing the medicament. The use of these microspheres provided an improvement in the controlled release of medicaments by utilizing the inherent biodegradability of the polymer to improve the release of the medicament and provide a more even, controlled level of medication. However, in some cases, biodegradable polymers under in vivo conditions can have an initial level of medicament release, which is too high or too low, and after a period of hydration can substantially degrade to thereby limit the effective life of the controlled release microspheres. Therefore, a need exists for a means of modulating the controlled release of medicament from a biodegradable polymer to provide a higher level of initial medicament release and to provide longer periods of fairly consistent medicament release levels in vivo.